A sodium-ion battery cathode material, its preparation method and application

Abstract

A sodium-ion battery cathode material, its preparation method, and its application are disclosed. The preparation method includes mixing a source M and a sodium source, followed by a first sintering, carbonization, high-entropy coating, and a second sintering to obtain the sodium-ion battery cathode material. The source M is a compound containing M, wherein M is selected from any three or more combinations of Ni, Mn, Cu, Fe, Co, Ti, Mg, B, Al, Zn, and Ca. The above preparation method is simple to operate, and the obtained sodium-ion battery cathode material has the characteristics of low surface alkalinity, few impurities, smooth and rounded morphology, and small specific surface area. Batteries prepared using this material have high capacity and excellent cycle stability.

Description

Technical Field

[0001] This application belongs to the field of battery technology, and in particular relates to a sodium-ion battery cathode material, its preparation method and application. Background Technology

[0002] Currently, the energy crisis and resource scarcity are becoming increasingly severe, prompting the nation to propose the goal of "carbon neutrality and carbon peaking," and vigorously develop new energy sources. Faced with this future vision, alkali metal ion rechargeable batteries have emerged as a promising option, attracting attention from companies worldwide. Among these, lithium-ion batteries have the most mature technology and applications; however, with continuous market development, lithium resources are becoming increasingly scarce, leading to soaring prices. Furthermore, the low abundance and uneven global distribution of lithium ore resources pose a significant obstacle to the development of new energy sources. In comparison, sodium, due to its abundant reserves and lower cost, and the similarity in working principles and high degree of overlap in production technology and tools between sodium-ion and lithium-ion batteries, is poised to become an excellent alternative to lithium-ion batteries in the future.

[0003] In sodium-ion batteries, the cathode material is crucial to both battery performance and cost advantages. Current research primarily focuses on three main types of cathode materials: layered transition metal oxides, polyanionic cathodes, and Prussian blue cathodes. Among these, O3-phase layered transition metal oxide cathodes have attracted significant attention due to their ease of synthesis and excellent capacity performance, with a theoretical specific capacity reaching 210 mAh / g. However, they also present several significant challenges. The primary issue is the high residual alkali on the surface of the O3-phase layered sodium electrode, leading to a high pH and facilitating gelation and severe gas generation during subsequent preparation. Furthermore, the surface instability of the O3-phase layered sodium electrode results in poor cycle stability.

[0004] There is currently no effective solution to the above problems.

[0005] Application content

[0006] The purpose of this application is to overcome the shortcomings of the prior art and provide a sodium-ion battery cathode material with low surface residual alkali content, high energy density and excellent cycle performance when applied to batteries, as well as its preparation method and application.

[0007] To achieve the above objectives, in a first aspect of this application, a method for preparing a sodium-ion battery cathode material is provided, the method comprising the following steps:

[0008] The M source and sodium source were mixed and sintered in one step to obtain a one-time sintered product;

[0009] The primary sintering product is sequentially subjected to carbonization treatment, high-entropy coating treatment, and secondary sintering treatment to obtain sodium-ion battery cathode material.

[0010] The M source is a compound containing M, wherein M is selected from any three or more combinations of Ni, Mn, Cu, Fe, Co, Ti, Mg, B, Al, Zn, and Ca;

[0011] The carbonization process involves placing the primary sintering product in an environment with a carbon dioxide concentration of 20-99%, a relative humidity of 5-30%, and a temperature of 15-50°C for carbonization to obtain the carbonized product.

[0012] The high-entropy coating process involves reacting the carbonization product with five or more metal ions whose ionic radii differ by less than 15% to form a high-entropy coating layer, wherein the high-entropy coating layer accounts for 0.2-1.2% of the mass of the carbonization product.

[0013] This application provides a method for preparing a sodium-ion battery cathode material. By sequentially carbonizing and high-entropy coating the primary sintering product, and controlling the mass ratio of the high-entropy coating layer to the carbonized product, the method can solve the problems of high residual alkali and poor cycle performance that conventional non-metallic and metal oxide coatings of cathode materials fail to address. The sodium-ion battery cathode material prepared using this method has a small specific surface area, a smooth, dense, and stable surface coating, low residual alkali, and a moderately thick high-entropy coating layer. When applied to batteries, it can reduce gas generation during cell use, suppress side reactions between the surface and the electrolyte, stabilize the internal structure of the cathode material particles, and reduce the dissolution of bulk sodium, thereby resulting in a battery with high energy density and excellent cycle performance.

[0014] Specifically, the surface of O3-phase layered sodium-ion battery cathode materials has a high residual alkali content, which mainly consists of sodium hydroxide and sodium carbonate, with sodium hydroxide being more prominent. By placing the product after primary sintering in a carbonization chamber with specific carbon dioxide concentration, relative humidity, and temperature for carbonization treatment, the conversion of sodium hydroxide to sodium carbonate on the cathode material surface can be completed relatively quickly. Compared to sodium hydroxide, which easily absorbs moisture and carbon dioxide from the air, causing further Na precipitation between the cathode material layers, sodium carbonate is more stable and can be used as a temporary coating layer to protect the cathode material. However, sodium carbonate has a large specific surface area and will also absorb water, and it has an adverse effect on gas production. Therefore, after carbonization treatment, a high-entropy coating treatment is combined to remove sodium carbonate. During the high-entropy coating process, five or more metal ions with radii differing by less than 15% react with sodium carbonate on the surface of the carbonization product to form a high-entropy coating layer. This high-entropy coating layer is a high-entropy infinite solid solution coating layer. The disordered occupancy of the metal ions in the coating layer can make the coating layer structure more stable, effectively isolating harmful substances from the cathode material, thereby reducing the surface sodium carbonate while forming a protective coating.

[0015] In one embodiment, the structural formula of the primary sintering product is Na.x MO₂, where 0 < x ≤ 1, and M is selected from any combination of three or more of Ni, Mn, Cu, Fe, Co, Ti, Mg, B, Al, Zn, and Ca.

[0016] In one embodiment, the M source is an oxide, hydroxide, or carbonate containing M.

[0017] In one embodiment, the sodium source is at least one of sodium carbonate, sodium hydroxide, or sodium acetate.

[0018] In one embodiment, the carbonization treatment is as follows: placing the primary sintered product in an environment with a carbon dioxide concentration of 40 - 90%, a relative humidity of 8 - 20%, and a temperature of 20 - 30°C for carbonization to obtain a carbonized treatment product.

[0019] In one embodiment, the carbonization treatment is as follows: placing the primary sintered product in an environment with a carbon dioxide concentration of 50 - 60%, a relative humidity of 10 - 15%, and a temperature of 20 - 30°C for carbonization to obtain a carbonized treatment product.

[0020] In one embodiment, the carbonization treatment time is 6 - 10 days.

[0021] During the carbonization treatment, carbon dioxide can provide raw materials for the reaction. Controlling a certain relative humidity is because the conversion of sodium hydroxide to sodium carbonate requires the participation of water, otherwise the reaction proceeds slowly and the efficiency is extremely low; by selecting to carbonize in an environment with a carbon dioxide concentration of 40 - 90%, a relative humidity of 8 - 20%, and a temperature of 20 - 30°C, especially when carbonizing in an environment with a carbon dioxide concentration of 50 - 60%, a relative humidity of 10 - 15%, and a temperature of 20 - 30°C, the purpose of more complete reaction, that is, lower sodium hydroxide content on the surface, and avoiding the precipitation of sodium between the layers of the cathode material and stably forming the cathode material can be achieved simultaneously.

[0022] In one embodiment, the high-entropy coating layer accounts for 0.5 - 1% of the mass of the carbonized treatment product.

[0023] As the mass percentage of the high-entropy coating layer in the carbonized treatment product increases, the residual alkali content on the surface of the obtained cathode material will show a gradually decreasing trend. However, when the mass percentage of the high-entropy coating layer in the carbonized treatment product continues to increase, the decreasing trend of the obtained residual alkali content is limited, and on the contrary, due to the overly thick high-entropy coating layer, it will affect the sodium ion deintercalation process during the actual use of the subsequent prepared battery, resulting in a decrease in capacity and even a significant decrease in the cycling performance. Therefore, when the high-entropy coating layer in the present invention accounts for 0.2 - 1.2% of the mass of the carbonized treatment product, especially 0.5 - 1%, the comprehensive performance of the obtained cathode material and the subsequent applied battery is more excellent.

[0024] In one embodiment, the carbonization product is reacted with seven metal ions whose ionic radii differ by less than 15% to form a high-entropy coating layer.

[0025] In one embodiment, the seven ions are manganese, titanium, magnesium, copper, scandium, iron, and tin.

[0026] In one embodiment, the molar ratio of manganese, titanium, magnesium, copper, scandium, iron, and tin is manganese:titanium:magnesium:copper:scandium:iron:tin = (0.35-0.45):(0.05-0.15):(0.05-0.15)(0.05-0.15):(0.03-0.07):(0.15-0.25):(0.03-0.07).

[0027] In the high-entropy coating process, different high-entropy coatings are formed by reacting with different metal ions. The high-entropy coating is a multi-element metal oxide system. Different components in the system can have different crystal structures, thus forming a stable solid solution, which in turn stabilizes the material structure. Furthermore, the introduction of metal ions can increase the interlayer spacing of sodium ions and improve the diffusion rate of sodium ions in the crystal structure. When the metal ions are further selected as manganese, titanium, magnesium, copper, scandium, iron, and tin, especially when the molar ratio of the seven is selected as manganese:titanium:magnesium:copper:scandium:iron:tin = (0.35-0.45):(0.05-0.15):(0.05-0.15)(0.05-0.15):(0.03-0.07):(0.15-0.25):(0.03-0.07), the resulting cathode material, when applied to the preparation of batteries, produces batteries with superior cycle stability.

[0028] After reacting the compounds of the above seven elements with sodium carbonate on the surface of the carbonization product, i.e., performing high-entropy coating treatment, the structural formula of the substance in the resulting high-entropy coating layer is NaMn. a Cu b Fe c Mg d Ti e Sn f Sc g O2, where a:b:c:d:e:f:g=(0.35-0.45):(0.05-0.15):(0.15-0.25)(0.05-0.15):(0.05-0.15):(0.03-0.07):(0.03-0.07).

[0029] In one embodiment, the reaction in the high-entropy coating process is carried out by dry ball milling or wet ball milling;

[0030] The dry ball milling process involves mixing and ball milling compounds containing the corresponding metal ions, followed by mixing and ball milling with the carbonization product.

[0031] The wet ball milling process involves mixing a compound containing the corresponding metal ions with the carbonization product, dissolving the mixture in water, and then ball milling it. After ball milling, the mixture is dried.

[0032] In one embodiment, in the dry ball milling, the compound containing the corresponding metal ions is the corresponding metal oxide. For example, when the seven ions selected are manganese, titanium, magnesium, copper, scandium, iron and tin, the titanium oxide, manganese oxide, magnesium oxide, copper oxide, scandium oxide, iron oxide and tin oxide are mixed and ball-milled and then mixed and ball-milled with the carbonization product.

[0033] In the wet ball milling process, the compound containing the corresponding metal ions is the corresponding metal chloride or nitrate. For example, when the seven ions selected are manganese, titanium, magnesium, copper, scandium, iron and tin, manganese nitrate, magnesium nitrate, copper nitrate, scandium nitrate, iron nitrate, titanium chloride, tin chloride and carbonization product are mixed, dissolved in water and ball milled, and then dried after ball milling.

[0034] In one embodiment, in the dry ball milling, the ball milling speed is 300-400 r / min, and the ball milling time is 2-6 h;

[0035] In the wet ball milling process, the ball milling speed is 300-400 r / min, and the milling time is 2-6 h.

[0036] In one embodiment, M is Ni, Mn, Fe, or Cu.

[0037] In one embodiment, the molar ratio of Ni, Mn, Fe and Cu is Ni:Mn:Fe:Cu = (0.20-0.28):(0.40-0.60):(0.10-0.20):(0.02-0.08).

[0038] Different primary sintering products yielded varying degrees of residual alkali reduction during subsequent processing, resulting in different battery capacity and cycle performance levels when applied to battery fabrication. When M was further selected as Ni, Mn, Fe, and Cu, especially when the molar ratio of Ni:Mn:Fe:Cu was Ni:Mn:Fe:Cu = (0.20-0.28):(0.40-0.60):(0.10-0.20):(0.02-0.08), the elements could interact to enhance the stability of the product, resulting in excellent battery capacity and cycle performance.

[0039] In one embodiment, the temperature of the first sintering is 800-1000°C, the time is 10-24 hours, and the atmosphere is any one or two of air, oxygen, or nitrogen.

[0040] For example, the temperature of the first sintering can be 800℃, 850℃, 900℃, 950℃, or 1000℃, and the time can be 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h, 20h, 21h, 22h, 23h, or 24h.

[0041] In one embodiment, the temperature of the first sintering is 900°C, the time is 15 hours, and the atmosphere is air.

[0042] In one embodiment, the secondary sintering temperature is 900-1000℃, the time is 5-15h, and the atmosphere is any one or two of oxygen, nitrogen, or argon.

[0043] For example, the temperature of the first sintering can be 900℃, 950℃, or 1000℃, and the time can be 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, or 15h.

[0044] In one embodiment, the temperature of the first sintering is 930°C, the time is 6 hours, and the atmosphere is argon.

[0045] In a second aspect, this application provides a sodium-ion battery cathode material, which is prepared using the preparation method described in this application.

[0046] In a third aspect, this application provides a positive electrode sheet comprising the sodium-ion battery positive electrode material described in this application.

[0047] In a fourth aspect, this application provides a sodium-ion battery, wherein the sodium ions comprise the positive electrode sheet described in this application.

[0048] Compared with the prior art, the beneficial effects of this application are as follows:

[0049] The sodium-ion battery cathode material prepared by the method provided in this application has the characteristics of low surface alkalinity, few impurities, smooth and rounded morphology, and small specific surface area. During the cathode material slurry mixing process, the low alkalinity surface helps avoid gelation of the slurry, facilitating subsequent coating and benefiting the preparation of the battery cathode sheet. Furthermore, the fewer alkaline impurities on the surface and the stable solid solution coating layer reduce gas generation during cell use, suppress side reactions between the surface and the electrolyte, stabilize the internal structure of the cathode material particles, reduce the dissolution of bulk sodium, and improve the cycle stability of the material. At the same time, the preparation method provided in this application is simple to operate and conducive to practical production. Attached Figure Description

[0050] Figure 1 Here is an SEM image of the carbonization product in Example 1;

[0051] Figure 2 Here is a SEM image of the cathode material in Example 1;

[0052] Figure 3 The images show the XRD patterns of the cathode materials in Examples 1 and 2.

[0053] Figure 4 This is a SEM image of the cathode material in Example 2. Detailed Implementation

[0054] To better illustrate the purpose, technical solution, and advantages of this application, the following will provide further explanation of this application in conjunction with specific embodiments.

[0055] Unless otherwise specified, the raw materials used in this application are conventional commercially available raw materials, and the raw materials used in the parallel embodiments or comparative examples in this application are the same.

[0056] Example 1

[0057] This application provides a sodium-ion battery cathode material, and the preparation method of the sodium-ion battery cathode material includes the following steps:

[0058] (1) Nickel oxide, manganese trioxide, ferric oxide, copper oxide, and sodium carbonate were mixed in a molar ratio of Ni, Fe, Mn, Cu, and Na of 0.20:0.15:0.60:0.05:0.95 and placed in a crucible. The mixture was then sintered at 900℃ for 15 hours in air. After sintering, the mixture was pulverized to obtain the first sintered product: Na 0.95 Ni 0.20 Fe 0.15 Cu 0.05 Mn 0.60 O2;

[0059] (2) The first sintered product was spread evenly on a 50*50cm tray and placed in a carbonization box. The temperature inside the box was adjusted to 25℃, the relative humidity to 10%, and the carbon dioxide concentration to 50%. The first sintered product was exposed to the carbonization box for 7 days to undergo conversion, and the carbonized product was obtained. Its morphology is shown in the figure below. Figure 1 As shown;

[0060] (3) The mass of each metal element nano-oxide raw material (nano-titanium oxide, nano-manganese oxide, nano-magnesium oxide, nano-copper oxide, nano-scandium oxide, nano-iron oxide, nano-tin oxide, wherein the molar ratio of manganese, titanium, magnesium, copper, scandium, iron, and tin is 0.4:0.1:0.1:0.1:0.05:0.1:0.05) is first placed in a planetary ball mill and premixed at 360 rpm / min for 2 h. Then the carbonized product is added and dry ball milled in the planetary ball mill at 360 r / min for 6 h.

[0061] (4) After ball milling, a second sintering was performed at 930℃ for 6 hours in an argon atmosphere. After sintering, Na was obtained. 0.95 Ni 0.20 Fe 0.15 Cu 0.05 Mn 0.60 The sodium-ion cathode material of O2@ZMSCT-dry has the following morphology: Figure 2 As shown, XRD is as follows Figure 3 As shown.

[0062] Example 2

[0063] This application provides a sodium-ion battery cathode material. The only difference between the preparation method of the sodium-ion battery cathode material and that of Example 1 is that step (4) involves wet coating, specifically:

[0064] The mass of each metal salt (manganese nitrate, magnesium nitrate, copper nitrate, scandium nitrate, ferric nitrate, titanium chloride, tin chloride, with the molar ratio of manganese, titanium, magnesium, copper, scandium, iron, and tin being 0.4:0.1:0.1:0.1:0.05:0.1:0.05) corresponding to the stoichiometric ratio of the high-entropy infinite solid solution coating layer of the carbonized product was dissolved in water and then dry-milled in a planetary ball mill at 360 rpm / min for 6 hours. After ball milling, the slurry was dried in a forced-air drying oven at 90°C for 2 hours.

[0065] The sodium ion cathode material Na obtained in Example 2 0.95 Ni 0.20 Fe 0.15 Cu 0.05 Mn 0.60 The morphological image of O2@ZMSCT-wet is as follows: Figure 4 As shown, the XRD pattern is as follows Figure 3 As shown.

[0066] Example 3

[0067] This application provides a sodium-ion battery cathode material. The only difference between the preparation method of the sodium-ion battery cathode material and that of Example 1 is that the carbon dioxide concentration in step (2) is 60%.

[0068] Example 4

[0069] This application provides a sodium-ion battery cathode material. The only difference between the preparation method of the sodium-ion battery cathode material and that of Example 1 is that the carbon dioxide concentration in step (2) is 40%.

[0070] Example 5

[0071] This application provides a sodium-ion battery cathode material. The only difference between the preparation method of the sodium-ion battery cathode material and that of Example 1 is that the carbon dioxide concentration in step (2) is 90%.

[0072] Example 6

[0073] This application provides a sodium-ion battery cathode material. The only difference between the preparation method of the sodium-ion battery cathode material and that of Example 1 is that the carbon dioxide concentration in step (2) is 20%.

[0074] Example 7

[0075] This application provides a sodium-ion battery cathode material. The only difference between the preparation method of the sodium-ion battery cathode material and that of Example 1 is that the carbon dioxide concentration in step (2) is 99%.

[0076] Example 8

[0077] This application provides a sodium-ion battery cathode material. The only difference between the preparation method of the sodium-ion battery cathode material and that of Example 1 is that the relative humidity in step (2) is 20%.

[0078] Example 9

[0079] This application provides a sodium-ion battery cathode material. The only difference between the preparation method of the sodium-ion battery cathode material and that of Example 1 is that the relative humidity in step (2) is 8%.

[0080] Example 10

[0081] This application provides a sodium-ion battery cathode material. The only difference between the preparation method of the sodium-ion battery cathode material and that of Example 1 is that the relative humidity in step (2) is 25%.

[0082] Example 11

[0083] This application provides a sodium-ion battery cathode material. The only difference between the preparation method of the sodium-ion battery cathode material and that of Example 1 is that the relative humidity in step (2) is 5%.

[0084] Example 12

[0085] This application provides a sodium-ion battery cathode material. The only difference between the preparation method of the sodium-ion battery cathode material and that of Example 1 is that the temperature in step (2) is 15°C.

[0086] Example 13

[0087] This application provides a sodium-ion battery cathode material. The only difference between the preparation method of the sodium-ion battery cathode material and that of Example 1 is that the temperature in step (2) is 50°C.

[0088] Example 14

[0089] This application provides a sodium-ion battery cathode material. The only difference between the preparation method of the sodium-ion battery cathode material and that of Example 1 is that in step (3), the mass of each metal element nano-oxide raw material corresponding to the stoichiometric ratio of the high-entropy infinite solid solution coating layer accounts for 1% of the mass of the carbonization product.

[0090] Example 15

[0091] This application provides a sodium-ion battery cathode material. The only difference between the preparation method of the sodium-ion battery cathode material and that of Example 1 is that in step (3), the mass of each metal element nano-oxide raw material corresponding to the stoichiometric ratio of the high-entropy infinite solid solution coating layer accounts for 0.2% of the mass of the carbonization product.

[0092] Example 16

[0093] This application provides a sodium-ion battery cathode material. The only difference between the preparation method of the sodium-ion battery cathode material and that of Example 1 is that in step (3), the mass of each metal element nano-oxide raw material corresponding to the stoichiometric ratio of the high-entropy infinite solid solution coating layer accounts for 1.2% of the mass of the carbonization product.

[0094] Example 17

[0095] This application provides a sodium-ion battery cathode material. The only difference between the preparation method of the sodium-ion battery cathode material and that of Example 1 is that in step (1), the molar ratio of Ni, Fe, Mn, Cu and Na elements is 0.20:0.15:0.55:0.10:0.95.

[0096] Example 18

[0097] This application provides a sodium-ion battery cathode material. The only difference between the preparation method of the sodium-ion battery cathode material and that of Example 1 is that in step (1), the molar ratio of Ni, Fe, Mn, Ti and Na elements is 0.20:0.15:0.60:0.05:0.95.

[0098] Example 19

[0099] This application provides a sodium-ion battery cathode material. The only difference between the preparation method of the sodium-ion battery cathode material and that of Example 1 is that in step (5), the molar ratio of manganese, titanium, magnesium, copper, scandium, iron and tin is 0.48:0.1:0.02:0.1:0.05:0.1:0.05.

[0100] Example 20

[0101] This application provides a sodium-ion battery cathode material. The only difference between the preparation method of the sodium-ion battery cathode material and that of Example 1 is that in step (5), the molar ratio of manganese, titanium, magnesium, copper, scandium and iron is 0.4:0.1:0.1:0.1:0.05:0.15.

[0102] Comparative Example 1

[0103] This application provides a sodium-ion battery cathode material in a comparative example. The only difference between the preparation method of the sodium-ion battery cathode material and that of Example 1 is that the carbonization treatment in step (2) is not performed.

[0104] Comparative Example 2

[0105] This application provides a sodium-ion battery cathode material in a comparative example. The only difference between the preparation method of the sodium-ion battery cathode material and that of Example 1 is that the high-entropy coating treatment in step (3) is not performed.

[0106] Comparative Example 3

[0107] This application provides a sodium-ion battery cathode material in comparison. The only difference between the preparation method of the sodium-ion battery cathode material and Example 1 is that the carbon dioxide concentration in step (2) is 100%.

[0108] Comparative Example 4

[0109] This application provides a sodium-ion battery cathode material in comparison. The only difference between the preparation method of the sodium-ion battery cathode material and Example 1 is that the carbon dioxide concentration in step (2) is 10%.

[0110] Comparative Example 5

[0111] This application provides a sodium-ion battery cathode material in comparative example. The only difference between the preparation method of the sodium-ion battery cathode material and Example 1 is that the relative humidity in step (2) is 60%.

[0112] Comparative Example 6

[0113] This application provides a sodium-ion battery cathode material in comparative example. The only difference between the preparation method of the sodium-ion battery cathode material and Example 1 is that the relative humidity in step (2) is 3%.

[0114] Comparative Example 7

[0115] This application provides a sodium-ion battery cathode material in comparison. The only difference between the preparation method of the sodium-ion battery cathode material and Example 1 is that in step (3), the mass of each metal element nano-oxide raw material corresponding to the stoichiometric ratio of the high-entropy infinite solid solution coating layer accounts for 1.5% of the mass of the carbonization product.

[0116] Comparative Example 8

[0117] This application provides a sodium-ion battery cathode material in comparison. The only difference between the preparation method of the sodium-ion battery cathode material and Example 1 is that in step (3), the mass of each metal element nano-oxide raw material corresponding to the stoichiometric ratio of the high-entropy infinite solid solution coating layer accounts for 0.1% of the mass of the carbonization product.

[0118] Comparative Example 9

[0119] This application provides a sodium-ion battery cathode material in a comparative example. The only difference between the preparation method of the sodium-ion battery cathode material and that of Example 1 is that in step (5), the molar ratio of potassium, titanium, magnesium, copper, scandium, iron and tin is 0.4:0.1:0.1:0.1:0.05:0.1:0.05.

[0120] Comparative Example 10

[0121] This application provides a sodium-ion battery cathode material in comparison. The only difference between the preparation method of the sodium-ion battery cathode material and that of Example 1 is that in step (1), the molar ratio of Ni, Fe, Sn, Ti and Na elements is 0.20:0.15:0.60:0.05:0.95.

[0122] Example 1

[0123] This application demonstrates the effectiveness of testing the residual alkali content on the surface of the sodium-ion cathode materials prepared in Examples 1-20 and Comparative Examples 1-10. Specifically, 1g of cathode material was taken from each sample and dissolved in 100mL of ultrapure water in an Erlenmeyer flask. After stirring with the Erlenmeyer flask closed for 30min, the mixture was immediately filtered to obtain the filtrate. 5mL of the filtrate from each sample was transferred and titrated with 0.05mol / L standard hydrochloric acid solution on a potentiometric titrator to test the residual alkali content on the sample surface. The test results are shown in Table 1.

[0124] Table 1

[0125]

[0126]

[0127] As can be seen from Table 1, when the technical solution of this application is adopted, the surface residual alkali content of the obtained sodium ion cathode material is low, wherein the sodium hydroxide content is below 2.0254%, the sodium carbonate content is below 1.2356%, and the sodium ion content is below 1.6141%.

[0128] As can be seen from Example 1 and Comparative Examples 1-2, regardless of whether carbonization or high-entropy coating is performed, the sodium ion content on the surface of the obtained cathode material increases significantly, by 84.80-115.87% compared to Example 1. That is, only with the combined effect of carbonization and coating can the residual sodium be reduced to a lower level, and the effect of a single treatment is not as good as the combined effect of the two.

[0129] As can be seen from Examples 1 and 2, compared with nanoscale dry coating, liquid phase wet coating has more advantages in reducing residual alkali. On the one hand, this is because liquid phase coating can form a more uniform high-entropy infinite solid solution coating layer on the surface, which can more effectively prevent the loss of bulk Na. On the other hand, because residual alkali can dissolve in water in a liquid phase environment, it also reduces a small amount of residual sodium during the ball milling stage.

[0130] As can be seen from Examples 1, 3-7 and Comparative Examples 3-4, the concentration of carbon dioxide in the carbonization process affects the residual alkali content. When the carbon dioxide content gradually increases, the residual alkali content shows a trend of first decreasing and then increasing. When the concentration of carbon dioxide in the carbonization process is further selected to be 40-90%, the sodium ion content in the obtained product is below 1.3585%.

[0131] As can be seen from Examples 1, 8-11, and Comparative Examples 5-6, the relative humidity during carbonization also affects the residual alkali content. When the humidity in Comparative Example 6 is too low, although the sodium carbonate content is low, the sodium hydroxide content is high, resulting in a relatively high overall residual alkali content. This is because the sodium hydroxide on the surface cannot react fully due to the low humidity. When the humidity in Comparative Example 5 is too high, the sodium ion content also increases by 132.75% compared to Example 1. This is because the increase in humidity leads to the precipitation of Na between the material layers, thus causing a further increase in the residual alkali on the surface.

[0132] As can be seen from Examples 1 and 12-13, the temperature selection in the carbonization process also affects the residual alkali content. If the temperature is too low, the reaction rate slows down and the residual alkali increases to a certain extent. If the temperature is too high, more Na is precipitated to a certain extent, resulting in a high residual alkali content.

[0133] As can be seen from Examples 1, 14-16 and Comparative Examples 7-8, the mass ratio of the high-entropy coating layer to the carbonization product also affects the surface residual alkali content of the product. If the mass ratio of the high-entropy coating layer is too large, although more surface residual sodium will be reacted, the electrical performance will be reduced due to the excessive coating thickness.

[0134] As can be seen from Examples 1 and 17-18, the structural formula of the primary sintering product is different, and the surface residual alkali content will also be different. In Example 17, increasing the Cu content can improve the water stability of the material, but it will cause a decrease in battery capacity. In Example 18, replacing Cu with Ti will reduce air stability and increase residual alkali.

[0135] As can be seen from Examples 1, 19-20 and Comparative Example 9, the metal ions selected in the high-entropy coating treatment also have a difference in the residual alkali content on the surface.

[0136] As can be seen from Examples 1, 17-18 and Comparative Example 10, the type selection and ratio in M ​​also affect the surface residual alkali content.

[0137] In addition, the morphology of the carbonization product in Example 1 is as follows: Figure 1 As shown, the morphology after secondary sintering is as follows: Figure 2 As shown, XRD is as follows Figure 3 As shown, from Figure 1 As can be seen, after carbonization, the surface of the cathode material contains a large amount of sodium carbonate impurities. After further coating and sintering, the surface of the material becomes like... Figure 2-3 The surface becomes smooth with a significant reduction in impurities. This indicates that the present invention's method of using a carbonization box to convert sodium hydroxide on the surface of the positive electrode material into sodium carbonate, followed by coating and removal at high temperatures, is feasible and can achieve the effect of reducing residual alkali on the surface.

[0138] Example 2

[0139] The effect example of this application is to apply the sodium-ion positive electrode materials prepared in Examples 1-20 and Comparative Examples 1-10 to a battery, and the performance of the battery is as follows: The positive electrode materials prepared in Examples 1-20 and Comparative Examples 1-10 are mixed with binder and conductive carbon black in a ratio of 90:5:5, NMP solvent is added and stirred, coated on a current collector and dried and rolled to obtain a positive electrode sheet, and the positive electrode sheet and sodium negative electrode sheet are used to make a sodium-ion battery, and the performance is tested at 1.5 to 4.2V. The test results are shown in Table 2.

[0140] Table 2

[0141]

[0142]

[0143] As can be seen from Table 1, when the technical solution of this application is adopted, the sodium-ion battery has a high first-cycle discharge capacity of over 151.5 mAh / g and a high cycle retention rate of over 91.7% after 50 cycles at 1C.

[0144] As can be seen from Example 1 and Comparative Examples 1-2, the first-cycle discharge capacity and the cycle retention rate of the battery after 50 cycles at 1C are significantly reduced, regardless of whether carbonization or high-entropy coating is performed. This is because both carbonization and coating contribute to the reduction of residual alkali, which in turn reduces surface side reactions, protects the internal structure of the particles, and improves the cycle performance of the material.

[0145] As can be seen from Examples 1, 3-7 and Comparative Examples 3-4, the concentration of carbon dioxide during carbonization treatment affects the first-cycle discharge capacity and the cycle retention rate of the battery after 50 cycles at 1C. When the carbon dioxide content is too high, not only does the residual alkali content on the surface of the obtained sodium ion cathode material increase, but the capacity and cycle performance of the obtained battery also show a downward trend. When the carbon dioxide content is too low, it is insufficient to convert sodium hydroxide, resulting in a significant deterioration in the performance of the obtained battery.

[0146] As can be seen from Examples 1, 8-11, and Comparative Examples 5-6, the relative humidity during carbonization also affects the battery's first discharge capacity and 50-cycle retention rate at 1C. When the humidity in Comparative Example 6 is too low, the battery's first discharge capacity and 50-cycle retention rate at 1C are significantly lower than those in Example 1. When the humidity in Comparative Example 5 is too high, the battery's first discharge capacity and 50-cycle retention rate at 1C also show a significant downward trend compared to Example 1.

[0147] As can be seen from Examples 1 and 12-13, the temperature selection during carbonization also affects the battery's first discharge capacity and 50-cycle retention rate at 1C. Temperatures that are too high or too low will affect the reaction rate, leading to differences in capacity and cycle retention rate.

[0148] As can be seen from Examples 1, 14-16, and Comparative Examples 7-8, the mass ratio of the high-entropy coating layer to the carbonization product also affects the battery's first-cycle discharge capacity and 50-cycle retention rate at 1C. Although it was found in Effect Example 1 that increasing the mass ratio of the high-entropy coating layer to the carbonization product effectively reduced the residual alkali content on the cathode material surface, the reduction effect was not significant with further increases in the mass ratio; instead, the battery capacity decreased significantly. If the mass ratio of the coating layer continued to increase, the cycle performance also showed a downward trend. This is because a large coating amount leads to an excessively thick coating layer on the material surface, affecting the Na... + The insertion / extraction process causes a decrease in capacity;

[0149] As can be seen from Examples 1, 17-18 and Comparative Example 10, the structural formulas of the products sintered in one step are different, and the first discharge capacity and the cycle retention rate of the battery after 50 cycles at 1C are also different.

[0150] As can be seen from Examples 1, 19-20 and Comparative Example 9, the metal ions selected in the high-entropy coating treatment also affect the battery's first discharge capacity and the cycle retention rate after 50 cycles at 1C.

Claims

1. A method for preparing a sodium-ion battery cathode material, characterized in that, The preparation method includes the following steps: The M source and sodium source were mixed and sintered in one step to obtain a one-time sintered product; The primary sintering product is sequentially subjected to carbonization treatment, high-entropy coating treatment, and secondary sintering treatment to obtain sodium-ion battery cathode material. The M source is a compound containing M, wherein M is selected from any three or more combinations of Ni, Mn, Cu, Fe, Co, Ti, Mg, B, Al, Zn, and Ca. The carbonization process involves placing the primary sintering product in an environment with a carbon dioxide concentration of 20-99%, a relative humidity of 5-30%, and a temperature of 15-50°C for carbonization to obtain the carbonized product. The high-entropy coating process involves reacting the carbonization product with six or seven metal ions whose ionic radii differ by less than 15% to form a high-entropy coating layer, wherein the high-entropy coating layer accounts for 0.2-1.2% of the mass of the carbonization product. The six metal ions with ionic radii differing by less than 15% are manganese, titanium, magnesium, copper, scandium, and iron; the seven metal ions with ionic radii differing by less than 15% are manganese, titanium, magnesium, copper, scandium, iron, and tin.

2. The preparation method according to claim 1, characterized in that, The carbonization process involves placing the primary sintering product in an environment with a carbon dioxide concentration of 40-90%, a relative humidity of 8-20%, and a temperature of 20-30°C for carbonization to obtain the carbonized product.

3. The preparation method according to claim 2, characterized in that, The carbonization process involves placing the primary sintering product in an environment with a carbon dioxide concentration of 50-60%, a relative humidity of 10-15%, and a temperature of 20-30°C to carbonize it, thereby obtaining the carbonized product.

4. The preparation method according to claim 1, characterized in that, The high-entropy coating layer accounts for 0.5-1% of the mass of the carbonization product.

5. The preparation method according to claim 1, characterized in that, When the carbonization product is reacted with the seven metal ions whose ionic radii differ from each other by less than 15% to form a high-entropy coating layer, the molar ratio of manganese, titanium, magnesium, copper, scandium, iron and tin is manganese:titanium:magnesium:copper:scandium:iron:tin = (0.35-0.45):(0.05-0.15):(0.05-0.15)(0.05-0.15):(0.03-0.07):(0.15-0.25):(0.03-0.07).

6. The preparation method according to claim 1, characterized in that, The reaction in the high-entropy coating process is carried out by dry ball milling or wet ball milling. The dry ball milling process involves mixing and ball milling compounds containing the corresponding metal ions, followed by mixing and ball milling with the carbonization product. The wet ball milling process involves mixing a compound containing the corresponding metal ions with the carbonization product, dissolving the mixture in water, and then ball milling it. After ball milling, the mixture is dried.

7. The preparation method according to claim 1, characterized in that, M is Ni, Mn, Fe, and Cu.

8. The preparation method according to claim 7, characterized in that, The molar ratio of Ni, Mn, Fe and Cu is Ni:Mn:Fe:Cu = (0.20-0.28):(0.40-0.60):(0.10-0.20):(0.02-0.08).

9. The preparation method according to claim 1, characterized in that, The sintering temperature is 800-1000℃, the time is 10-24h, and the atmosphere is any one or two of air, oxygen or nitrogen.

10. The preparation method according to claim 1, characterized in that, The secondary sintering temperature is 900-1000℃, the time is 5-15h, and the atmosphere is any one or two of oxygen, nitrogen or argon.

11. A sodium-ion battery cathode material, characterized in that, The sodium-ion battery cathode material is prepared using the preparation method described in any one of claims 1-10.

12. A positive electrode plate, characterized in that, The positive electrode sheet comprises the sodium-ion battery positive electrode material as described in claim 11.

13. A sodium-ion battery, characterized in that, The sodium-ion battery includes the positive electrode as described in claim 12.

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